* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download electric current
Survey
Document related concepts
Nanofluidic circuitry wikipedia , lookup
Cavity magnetron wikipedia , lookup
Power electronics wikipedia , lookup
Power MOSFET wikipedia , lookup
Resistive opto-isolator wikipedia , lookup
Switched-mode power supply wikipedia , lookup
Nanogenerator wikipedia , lookup
Electric charge wikipedia , lookup
Opto-isolator wikipedia , lookup
Surge protector wikipedia , lookup
Current mirror wikipedia , lookup
Transcript
Electric Current Chapter 20 Electricity and Energy Song Video Solids: Conductors, Insulators and Semiconductors Conductors: Insulators: mostly metals mostly nonmetal materials Semiconductors: metalloids Bonding in Metals The electron-sea model is a simple depiction of a metal as an array of positive ions surrounded by delocalized valence electrons. – Metals are good conductors of electricity because of the mobility of these delocalized valence electrons. – A metal also conducts heat well because 3 electrons can carry additional the mobile kinetic energy. Bonding in Metals 4 Semiconductors Metalloids: semiconducting elements Low electrical conductivity at room temperature Electrical conductivity increases with temp. Semiconductors Semiconducting elements form the basis of solid state electronic devices. Metalloids (such as silicon or germanium) are semiconducting elements whose electrical conductivity increases as temperature increases. Shocking! If you reach for a metal doorknob after walking across a carpet, you might see a spark. The spark is caused by electrons moving from your hand to the doorknob. Conductor! A material in which electrons are able to move easily is a conductor. The best electrical conductors are metals. Not a Conductor! A material in which electrons are not able to move easily is an insulator. Most plastics are insulators Charging Objects Rubbing two materials together can result in a transfer of electrons. Then one material is left with a positive charge and the other with an equal amount of negative charge. The process of transferring charge by touching or rubbing is called charging by contact. INDUCTION! Because electrical forces act at a distance, charged objects brought near a neutral object will cause electrons to rearrange their positions on the neutral object. The rearrangement of electrons on a neutral object caused by a nearby charged object is called charging by induction. Induction The balloon on the left is neutral. The balloon on the right is negatively charged. It produces a positively charged area on the sleeve by repelling electrons. Current and Potential The net movement of electric charges in a single direction is an electric current. In a metal wire, or any material, electrons are in constant motion in all directions. As a result, there is no net movement of electrons in one direction. Current and Voltage When an electric current flows in the wire, electrons continue their random movement, but they also drift in the direction that the current flows. Electric current is measured in amperes. Voltage difference In a similar way, electric charge flows from higher voltage to lower voltage. A voltage difference is related to the force that causes electric charges to flow. Voltage difference is measured in volts. Electric Circuits This figure shows an electric current doing work by lighting a lightbulb. A closed path that electric current follows is a circuit. If the circuit is broken by removing the battery, or the lightbulb, or one of the wires, current will not flow. Resistance As the electrons flow through the filament in a lightbulb, they bump into the metal atoms that make up the filament. In these collisions, some of the electrical energy of the electrons is converted into thermal energy. Eventually, the metal filament becomes hot enough to glow, producing radiant energy that can light up a dark room. Electric Current Electrons in motion. Current: The number of electrons that pass a specific point in a circuit in one second I = Q/t Circuit: electric current flows through a closed, continuous path. Electric Current The reason electric charge flows from one place to another is voltage. a. Voltage is the difference in electrical potential between two places where e¯ are flowing. b. Voltage is the “push” that makes electric charges move. c. Measured in volts (V). HIGH LOW Batteries are e¯ pumps. a. They provide a voltage difference to a circuit. b. Types: wet-cells & dry-cells Generating Electric Current Electrochemical cell: (battery) changes chemical energy into electric energy. Two types wet cell and dry cell. Thermocouples: a tool that uses differences in temperature to generate electric currents. Generator- next chapter but make alternating current Types of current Direct current: electrons that flow in the same direction in a wire. (DC) From batteries Alternating current: electrons that flow in different directions in a wire. (AC) From Generators Used in your home Transformers change AC to DC Measuring Electricity Current: Measured in Amperes or amps (A) Voltage: Measured in volts (V) Higher voltage, the more work the electrons can do. Measuring Electricity Resistance: the force opposing the flow of electrons. Measured in ohms Symbol is Greek letter omega Thicker wire- less resistance Longer wire- more resistance Conductors- low resistance Insulators- high resistance Ohm’s Law The relationship among current, voltage, and resistance. Ohm’s law states that the current in a circuit is equal to the voltage divided by the resistance I=V R V I R V Do the Math I R A car has a 12 volt system. The headlights are on a 10 amp circuit. How much resistance do they have? V Do the Math I R A car has a 12 volt system. The headlights are on a 10 amp circuit. How much resistance do they have? R =V / I R = 12 V / 10 amp R =1.2 V Do the Math I R Your house uses 120 volts. What amount of current would flow through a 20 ohm resistor? V Do the Math I R Your house uses 120 volts. What amount of current would flow through a 20 ohm resistor? I = V / R I = 120 V / 20 ohm I = 6 amperes (A) Electric power and energy Power: The rate at which electricity does work or provides energy The amount of electric power a device uses to do work is determined by its resistance. P= VxI (P) power = (V) voltage x (I) current in the circuit. Energy Formula for energy E=Pxt (E) energy used = (P) power x (t) time The SI unit for energy is a joule. Kilowatt-hour meters measure the electricity used in your home. (kWh) Electricity and Energy Song Video Write a Paragraph: (Ch 20) Investigate and explain the relationships among: current Voltage Resistance power Grade the paragraph Current – number of electrons that pass a specific point in a circuit in one second. Reason it flows is due to voltage. Voltage – is the push that makes the electric charge move Resistance – force opposing the flow of electrons (or current) Power – rate electricity does work. The amount of work is determined by its resistance.